The present invention generally relates to pneumatic transportation systems wherein vehicles are pneumatically propelled along a vehicle guideway by one or more vehicle propulsion plate extending into an air duct of the guideway. The invention more particularly relates to the manner of connecting a propulsion plate to a pneumatically propelled vehicle, and has particular application in respect to vehicles having horizontal stabilizing beams on the underside of the vehicle for counter-balancing torsional forces transmitted to the vehicle from the propulsion plate.
U.S. Pat. No. 4,658,732 issued to Oskar H. W. Coester (the Coester '732 patent) discloses a pneumatic transportation system wherein vehicles capable of transporting freight or passengers are propelled along an elevated vehicle guideway having an enclosed air duct beneath a trackway support platform. The vehicle is propelled by pneumatic propulsion forces acting against a propulsion plate in the guideway air duct, which in turn is connected to one of the vehicle's wheel trucks by a mast or pylon that passes through a longitudinal sealed guide slot in the guideway support platform. Also disclosed is the use of a horizontal stabilizing or traction beam connected between the pylon and the underside of the vehicle body to counteract the bending moment produced at the top of the vertical pylon by the horizontal propulsion forces on the propulsion plate attached to the bottom of the pylon. This beam reduces the tendency of the pneumatic propulsion forces to lift the vehicle truck wheels from the track, thereby increasing traction or contact between the track and the vehicle. This is especially important in transportation systems of this type, since the vehicles are relatively light as compared to vehicles having onboard motors or other onboard power sources.
While the pneumatically propelled vehicle shown in the Coester '732 patent would perform suitably along straight sections of guideway, its disclosed use of a stabilizing beam is not practical for pneumatic transportation systems having a guideway configuration employing horizontal curves. Specifically, the disclosed rigid connection between the stabilizing beam and propulsion plate of the vehicle would prevent the pylon from rotating with the wheel truck as the wheel truck enters a curve thereby preventing rotation of the wheel truck. The rigid connection between the pylon and stabilizing beam and the vehicle's wheel trucks would also cause the wheels of the wheel trucks to lose contact with the tracks of the guideway when the wheel trucks enter and exit vertical curves due to the inability of the wheel trucks to freely follow changes in gradients in the trackway.
Another difficulty with the wheel truck design shown in the Coester '732 patent relates to its conventional placement of the propulsion plate in a centered position relative to the wheel truck, that is, midway between truck wheels. This centered position results in small misalignments between the propulsion plate and air duct in horizontal curves of the guideway as well as misalignments between the vertical pylon and the support platform guide slot. These temporal misalignments require compensations in the sizing of the propulsion plate and guide slot which increase air leakage and reduce system efficiency. Furthermore, failure to keep the propulsion plate and pylon centered relative to the air duct and guide slot as the vehicle negotiates a horizontal curve increases wear on the seals of the propulsion plate and guide slot.
The present invention provides an improved propulsion plate connector system which overcomes the above-mentioned problems of propulsion plate and pylon alignment as a vehicle negotiates curved sections of the vehicle guideway of a pneumatic transportation system. The invention provides a mechanism for connecting the propulsion plate to the wheel truck of a pneumatically propelled vehicle in a manner that permits the vehicle to freely negotiate horizontal and vertical curves while maintaining contact between the truck wheels and the trackway, and while keeping the propulsion plate and its connecting pylon in a true centered position relative to the air duct and guide slot. Using the pylon connector system of the invention, a propulsion plate can be designed closer to the dimensions of the air duct (that is, with very small gaps between the edges of the propulsion plate and the walls of the guideway) resulting in reduced air flow across the propulsion plate. Maintaining a centered pylon as it passes through the guide slot will also reduce air leakage through the slot seal and slot seal wear.